Congressional parties are commonly regarded as highly unified legislative teams, but the Tea Party Caucus has revealed factional divisions with the Republican Party. Using annual ratings from 290 interest groups, we estimate the ideological locations of Republican legislators to map their party’s factional structure. We project a bipartite network of annual scores to relate interest groups by the similarity of their ratings and legislators by the similarity in which they have been rated. Cluster analysis identifies factions of moderate and extreme Republicans. Further investigation shows that Republican leaders withhold legislative rewards from both subgroups, but that moderates are denied disproportionately
